right, here's a complete guess ;-)
sd is your fixed disk device, fd is probably a floppy device, td is, I guess, a tape/cartridge type thing etc.
so you probably want to use the fixed disk as a root device - so type sd. then it needs to know which disk/partition to use - this is where it gets tricky. try sda - this will normally be the first disk device present in your machine, and seems like a good place to start. the only other thing it may want is a partition number. so you may end up with something like sda0, which would be the first partition on the first disk in your system.
hope that helps!
[This message has been edited by ben-fu (edited 09-06-2000).]